1) Field of the Invention
The present invention relates to a magnetic resistance memory and a writing method of the magnetic resistance memory.
2) Description of the Related Art
Magnetic resistance memory (MRAM: Magnetic Random Access Memory) is gaining ground in recent years as a next generation memory for its high speed and non-volatile properties. FIG. 5 is a schematic diagram of a basic principle of an MRAM. Each memory cell is formed of a non-magnetic layer 502 sandwiched between a first ferromagnetic layer 501 and a second ferromagnetic layer 503.
The first ferromagnetic layer 501 is a changeable ferromagnetic layer, of which the magnetization direction can be changed by passing an electric current, whereas the second ferromagnetic layer 503 is an unchangeable ferromagnetic layer, of which the magnetization direction remains constant. When the first ferromagnetic layer 501 and the second ferromagnetic layer 503 have a same magnetization direction, magnetic resistance between the first ferromagnetic layer 501 and the second ferromagnetic layer 503 decreases. When the first ferromagnetic layer 501 and the second ferromagnetic layer 503 have different magnetization directions, the magnetic resistance between the first ferromagnetic layer 501 and the second ferromagnetic layer 503 increases.
The MRAM memory cell stores information based on a degree of magnetic resistance, which is dependent on the magnetization direction of the first ferromagnetic layer 501, between the first ferromagnetic layer 501 and the second ferromagnetic layer 503. For instance, when the magnetic resistance is low, a one-bit data ‘0’ is stored, and when the magnetic resistance is high, a one-bit data ‘1’ is stored.
Data can be written to MRAM by passing an electric current in a destination memory cell to change the magnetization direction of the changeable ferromagnetic layer to a predetermined direction. A technology relating to the MRAM is disclosed in, for example, “MRAM”, URL: http://www.nanoelectronic.jp/kaitai/mram/, searched on Jul. 29, 2004.
However, writing data to MRAM requires a constant application of electric current to the destination memory cell, resulting in large power consumption.